In many optical local area networks (LAN) and backplanes that have a bus-type architecture, an optical repeater receives and combines optical signals from optical transmitters in system nodes, as well as amplifies and individually retransmits signals to optical receivers in the system nodes. In this prior art system, optical couplers are referred to as optical splitters and combiners which designate the functions being performed by these optical couplers.
FIG. 2 illustrates a prior art optical coupler in accordance with U.S. Pat. No. 4,913,508 that can perform the functions of the combiner and splitter of FIG. 1. Optical signals from optical fiber bundle 201 are coupled via optical coupler 203 to optical fiber 204. Similarly, an optical signal from optical fiber 204 is coupled to optical fiber 201 bundle. The cavity of optical coupler 203 forms the optical waveguide core of the optical coupler and is substantially circular. The cavity is filled with a material having a refractive index such that the resulting optical waveguide has a numerical aperture that substantially matches the numerical apertures of optical fiber 204 and optical fiber bundle 201.
One problem with the coupler of FIG. 2 is that there is no selfaligning mechanism to guarantee that the fibers of the optical fiber bundle will always have a particular arrangement within the optical coupler. This arrangement is necessary to assure that the optical communications characteristics of different optical fiber and coupler combinations are uniform. Such an alignment is also particularly important for field applications where the field personnel do not have access to sophisticated laboratory equipment that can verify the communication quality of the fiber and coupler combination. In addition, field personnel do not have the time to be sure that fibers are arranged in a particular way. Another problem with the coupler of FIG. 2 is that it does not have a low cost.